Highly stereoregular polypropylene with improved properties

ABSTRACT

Propylene polymers having a content of isotactic pentads (mmmm) higher than 97%, molecular weight distribution, expressed by the formula (a) ratio, equal to or higher than 6 and a value of formula (b) ratio equal to or lower than 5.5. The said polymers are prepared in the presence of a particular combination of Ziegler-Natta solid catalyst components and highly stereoregulating electron-donor compounds. Laminated articles, in particular bi-axially oriented films and sheets, can be prepared with the said polymers
 
{overscore (M)} w /{overscore (M)} n    (a)
 
{overscore (M)} z /{overscore (M)} w .   (b)

This application is the U.S. national phase of International ApplicationPCT/EP2003/008491, filed Jul. 30, 2003, claiming priority to EuropeanPatent Application 02017287.0, filed Aug. 1, 2002, and the benefit under35 U.S.C. 119(e) of U.S. Provisional Application No. 60/416,99 1, filedOct. 8, 2002; the disclosures of International ApplicationPCT/EP2003/00849 1, European Patent Application 02017287.0 and U.S.Provisional Application No. 60/416,99 1, each as filed, are incorporatedherein by reference.

The present invention relates to crystalline propylene polymers having ahigh level of chain stereoregularity, in particular a high content ofisotactic pentads, improved processability in the molten state and theprocess for preparation thereof.

It is known that, thanks to high stereospecificity levels reached by theZiegler-Natta catalysts, today one can prepare highly crystallinepropylene polymers having high mechanical properties and they are,therefore, adequate for the manufacture of articles with good stiffnessand mechanical resistance, even if they are small and thin. The commonused propylene polymers show high enough levels of melt strength, i.e.viscoelasticity in the molten state.

It is known that non-highly enough levels of melt strength of propylenepolymers cause an irregular deformation of the molten mass during theconversion processes with the subsequent problems related toworkability.

European patent application No. 573 862 discloses that melt strength canbe significantly improved by widening the molecular weight distributionof a polymer. According to the patent, the molecular weight distributionis at least 20. Consequently, the workability of highly crystallinepropylene polymers improves. However, the thickness profile andconsistency of the oriented films obtained from said propylene polymersare not totally satisfactory yet.

It has now been found that by using in polymerization, under suitableconditions, a particular combination of Ziegler-Natta solid catalystcomponents and highly stereoregulating electron-donor compounds (outsidedonors), it is possible to obtain propylene polymers still characterizedby high stiffness and other mechanical properties typical of highlycrystalline propylene polymers, but also by improved workability inspite of a medium broad molecular weight distribution. In particular,the advantages are that the present propylene polymers can be processedat a broad range of temperatures and thus are easier processable.

A further embodiment of the present invention, relates to biaxiallyoriented films or sheets comprising the said propylene polymers.

The advantage of laminated articles, in particular films and sheets, ofthe present invention is that they have good uniform thickness and alsohigher elongation at break and higher tensile stress at break.

The present laminated articles, in particular films or sheets, areespecially used in packaging of parcels, such as cigarette parcels, andin food packaging.

Therefore the present invention provides propylene polymers, preferablyhomopolymers, having the following features:

-   1) a content of isotactic pentads (mmmm), measured by NMR, higher    than 97%, preferably higher than 97.5%, more preferably higher than    98%;-   2) a molecular weight distribution, expressed by the ratio of weight    average molecular weight to number average molecular weight    ({overscore (M)}_(w)/{overscore (M)}_(n)), equal to or higher than    6, preferably from 6 to 11; and-   3) a value of ratio of z average molecular weight to weight average    molecular weight ({overscore (M)}_(z)/{overscore (M)}_(w)) equal to    or lower than 5.5, preferably equal to or lower than 5, more    preferably equal to or lower than 4.8.

Optionally the said propylene polymers can contain minor amounts ofcomonomers, like ethylene or C₄–C₁₀ α-olefins (examples of which are1-butene, 1-hexene, 3-methyl-1-pentene). Generally, when present, suchcomonomers do not exceed 5% by weight (preferably 2% by weight in thecase of ethylene) with respect to the total weight of the polymer.

Other preferred features for the polymers of the present invention are:

-   -   a stereoblock content up to 98° C. of 10% or lower measured by        the Temperature Raising Elution Fractionation (TREF) method;    -   a content of fraction soluble in xylene at room temperature        (about 23° C.) equal to or lower than 2.5% by weight, more        preferably equal to or lower than 2% by weight;    -   a Polydispersity Index (P.I.) of 6 or less, more preferably of        5.5 or less, in particular less than 5;    -   a value of the main elution peak temperature (measured by TREF)        higher than 114° C.;    -   a value of the fraction eluted up to 94° C. (TREF) equal to or        lower than 5%;    -   an MFR value from 0.1 to 50 g/10 min, more preferably from 1 to        30 g/10 min;

The preferred polymers according to the present invention have a meltingpoint of 164° C. or higher, more preferably of 165° C. or higher, suchas from 165 to 168° C.

The propylene polymers of the present invention can be obtained directlyin polymerization by using a Ziegler-Natta catalyst comprising:

-   -   a solid catalyst component comprising Mg, Ti, halogen and at        least two electron donor compounds, said catalyst component        being characterised by the fact that at least one of the        electron donor compounds, which is present in an amount from 15        to 50% by mol with respect to the total amount of electron-donor        compounds, is selected from esters of succinic acids which are        not extractable, under the conditions described below, for more        than 20% by mol (non-extractable succinates) and at least        another electron donor compound which is extractable, under the        same conditions, for more than 30% by mol (extractable electron        donor compounds);    -   an organo-metal compound;    -   a highly stereoregulating electron donor compound (outside        donor).

The said catalyst component is described in WO 02/30998.

As explained above, the solid catalyst component comprises, in additionto the above electron donor compounds, Ti, Mg and halogen. Inparticular, the catalyst component comprises a titanium compound, havingat least a Ti-halogen bond and the above mentioned electron donorcompounds supported on a Mg halide. The magnesium halide is preferablyMgCl₂ in active form, which is widely known from the patent literatureas a support for Ziegler-Natta catalysts. U.S. Pat. Nos. 4,298,718 and4,495,338 were the first to describe the use of said compounds inZiegler-Natta catalysis. It is known from said patents that themagnesium dihalides in active form used as support or co-support incomponents of catalysts for the polymerization of olefins arecharacterized by X-ray spectra in which the most intense diffractionline that appears in the spectrum of the non-active halide is diminishedin intensity and is replaced by a halo whose maximum intensity isdisplaced towards lower angles relative to that of the more intenseline.

The preferred titanium compounds are TiCl₄ and TiCl₃; furthermore; alsoTi-haloalcoholates of formula Ti(OR)_(n-y)X_(y) can be used, where n isthe valence of titanium, y is a number between 1 and n-1, X is halogenand R is a hydrocarbon radical having from 1 to 10 carbon atoms.

The preparation of the solid catalyst component can be carried outaccording to several methods, well known and described in the art.

According to a preferred method, the solid catalyst component can beprepared by reacting a titanium compound of formula Ti(OR)_(n-y)X_(y),where n is the valence of titanium and y is a number between 1 and n,preferably TiC₄, with a magnesium chloride deriving from an adduct offormula MgCl₂.pROH, where p is a number between 0.1 and 6, preferablyfrom 2 to 3.5, and R is a hydrocarbon radical having 1–18 carbon atoms.The adduct can be suitably prepared in spherical form by mixing alcoholand magnesium chloride in the presence of an inert hydrocarbonimmiscible with the adduct, operating under stirring conditions at themelting temperature of the adduct (100–130° C.). Then, the emulsion isquickly quenched, thereby causing the solidification of the adduct inform of spherical particles.

Examples of spherical adducts prepared according to said procedure aredescribed in U.S. Pat. No. 4,399,054 and U.S. Pat. No. 4,469,648. The soobtained adduct can be directly reacted with Ti compound or it can bepreviously subjected to thermal controlled dealcoholation (80–130° C.)so as to obtain an adduct in which the number of moles of alcohol isgenerally lower than 3 preferably between 0.1 and 2.5. The reaction withthe Ti compound can be carried out by suspending the adduct(dealcoholated or as such) in cold TiCl₄ (generally 0° C.); the mixtureis heated up to 80–130° C. and kept at this temperature for 0.5–2 hours.The treatment with TiCl₄ can be carried out one or more times. Theelectron donor compounds can be added during the treatment with TiCl₄.They can be added together in the same treatment with TiCl₄ orseparately in two or more treatments.

Regardless to the preparation method used, the final amount of the twoor more electron donor compounds is such that the molar ratio withrespect to the MgCl₂ is from 0.01 to 1, preferably from 0.05 to 0.5.

Among the non-extractable succinates mentioned above, particularlypreferred are the succinates of formula (I) below

in which the radicals R₁ and R₂, equal to, or different from, each otherare a C₁–C₂₀ linear or branched alkyl, alkenyl, cycloalkyl, aryl,arylalkyl or alkylaryl group, optionally containing heteroatoms; and theradicals R₃ and R₄ equal to, or different from, each other, are C₁–C₂₀alkyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionallycontaining heteroatoms with the proviso that at least one of them is abranched alkyl; said compounds being, with respect to the two asymmetriccarbon atoms identified in the structure of formula (I), stereoisomersof the type (S,R) or (R,S) that are present in pure forms or inmixtures.

R₁ and R₂ are preferably C₁–C₈ alkyl, cycloalkyl, aryl, arylalkyl andalkylaryl groups.

Particularly preferred are the compounds in which R₁ and R₂ are selectedfrom primary alkyls and in particular branched primary alkyls. Examplesof suitable R₁ and R₂ groups are methyl, ethyl, n-propyl, n-butyl,isobutyl, neopentyl, 2-ethylhexyl. Particularly preferred are ethyl,isobutyl, and neopentyl.

Particularly preferred are the compounds in which the R₃ and/or R₄radicals are secondary alkyls like isopropyl, sec-butyl, 2-pentyl,3-pentyl or cycloakyls like cyclohexyl, cyclopentyl, cyclohexylmethyl.

Examples of the above-mentioned compounds are the (S,R) (S,R) forms pureor in mixture, optionally in racemic form, of diethyl2,3-bis(trimethylsilyl)succinate, diethyl2,3-bis(2-ethylbutyl)succinate, diethyl 2,3-dibenzylsuccinate, diethyl2,3-diisopropylsuccinate, diisobutyl 2,3-diisopropylsuccinate, diethyl2,3-bis(cyclohexylmethyl)succinate, diethyl 2,3-diisobutylsuccinate,diethyl 2,3-dineopentylsuccinate, diethyl 2,3-dicyclopentylsuccinate,diethyl 2,3-dicyclohexylsuccinate.

Among the extractable electron donor compounds particularly preferredare the esters of mono or dicarboxylic organic acids such as benzoates,malonates, phthalates and succinates. Preferred are esters of aromaticcarboxylic acids.

Among malonates particularly preferred are those of formula (II):

where R₁ is H or a C₁–C₂₀ linear or branched alkyl, alkenyl, cycloalkyl,aryl, arylalkyl or alkylaryl group, R₂ is a C₁–C₂₀ linear or branchedalkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, R₃ andR₄, equal to, or different from, each other, are C₁–C₂₀ linear orbranched alkyl groups or C₃–C₂₀ cycloalkyl groups.

Preferably, R₃ and R₄ are primary, linear or branched C₁–C₂₀ alkylgroups, more preferably they are primary branched C₄–C₂₀ alkyl groupssuch as isobutyl or neopentyl groups.

R₂ is preferably, in particular when R₁ is H, a linear or branchedC₃–C₂₀ alkyl, cycloalkyl, or arylalkyl group; more preferably R₂ is aC₃–C₂₀ secondary alkyl, cycloalkyl, or arylalkyl group.

Preferred esters of aromatic carboxylic acids are selected from C₁–C₂₀alkyl or aryl esters of benzoic and phthalic acids, possiblysubstituted. The alkyl esters of the said acids being preferred.Particularly preferred are the C₁–C₆ linear or branched alkyl esters.Specific examples are ethylbenzoate, n-butylbenzoate, p-methoxyethylbenzoate, p-ethoxy ethylbenzoate, isobutylbenzoate, ethylp-toluate, diethyl phthalate, di-n-propyl phthalate, di-n-butylphthalate, di-n-pentyl phthalate, di-i-pentyl phthalate,bis(2-ethylhexyl)phthalate, ethyl-isobutyl phthalate, ethyl-n-butylphthalate, di-n-hexyl phthalate, di-isobutylphthalate.

The previously said organo-metal compound is preferably chosen amongalkyl-Al compounds and in particular among the trialkyl aluminumcompounds such as for example triethylaluminum, triisobutylaluminum,tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It isalso possible to use alkylaluminum halides, alkylaluminum hydrides oralkylaluminum sesquichlorides, such as AlEt₂Cl and Al₂Et₃Cl₃, possiblyin mixture with the above cited trialkylaluminums.

Suitable outside electron-donor compounds include certain silanes,ethers, esters, amines, heterocyclic compounds and ketones. Inparticular, suitable highly stereoregolating silanes are comprised inthe class having formula R_(a) ⁵R_(b) ⁶Si(OR⁷)_(c), where a and b areintegers from 0 to 2, c is an integer from 1 to 4 and the sum (a+b+c) is4; R⁵, R⁶ and R⁷ are alkyl, alkylen, cycloalkyl or aryl radicals with 1to 18 carbon atoms, optionally containing heteroatoms. Particularlypreferred are the silicon compounds in which at least one of R⁵ and R⁶is selected from branched alkyl and cycloalkyl groups with 3 to 10carbon atoms and R⁷ is a C₁–C₁₀ alkyl group, in particular methyl.Specific examples of preferred silanes are dicyclopentyldimethoxysilane,tert-hexyltrimethoxysilane and diisopropyldimethoxysilane.Dicyclopentyldimethoxysilane is particularly preferred.

The outside donor is used in such an amount to give a molar ratio of theorganoaluminum compound to said outside electron donor compound of from0.1 to 500, preferably from 1 to 300 and more preferably from 3 to 100.

The polymerisation process can be carried out according to knowntechniques, for example slurry polymerisation using as diluent an inerthydrocarbon solvent, or bulk polymerisation using the liquid monomer(for example propylene) as a reaction medium. Moreover, it is possibleto carry out the polymerisation process in gas-phase operating in one ormore fluidised or mechanically agitated bed reactors.

The polymerisation is generally carried out at temperature of from 20 to120° C., preferably of from 40 to 80° C. When the polymerisation iscarried out in gas-phase the operating pressure is generally between 0.5and 10 MPa, preferably between 1 and 6 MPa. In the bulk polymerisationthe operating pressure is generally between 1 and 8 Mpa, preferablybetween 1.5 and 5 MPa.

It is particular worth noting that the said broad range of values ofmolecular weight distribution is obtained in a single polymerisationstage, i.e. with a substantially monomodal distribution which allows toavoid any problem due to non homogeneity of the polymer product.

According to a preferred polymerisation process the polymers of thepresent invention can be produced by a gas-phase polymerisation processcarried out in at least two interconnected polymerisation zones. Thesaid type of process is illustrated in European patent application 782587.

In detail, the above-mentioned process comprises feeding one or moremonomer(s) to said polymerisation zones in the presence of catalystunder reaction conditions and collecting the polymer product from thesaid polymerisation zones. In the said process the growing polymerparticles flow upward through one (first) of the said polymerisationzones (riser) under fast fluidisation conditions, leave the said riserand enter another (second) polymerisation zone (downcomer) through whichthey flow downward in a densified form under the action of gravity,leave the said downcomer and are reintroduced into the riser, thusestablishing a circulation of polymer between the riser and thedowncomer.

In the downcomer high values of density of the solid are reached, whichapproach the bulk density of the polymer. A positive gain in pressurecan thus be obtained along the direction of flow, so that it becomes topossible to reintroduce the polymer into the riser without the help ofspecial mechanical means. In this way, a “loop” circulation is set up,which is defined by the balance of pressures between the twopolymerisation zones and by the head loss introduced into the system.

Generally, the condition of fast fluidization in the riser isestablished by feeding a gas mixture comprising the relevant monomers tothe said riser. It is preferable that the feeding of the gas mixture iseffected below the point of reintroduction of the polymer into the saidriser by the use, where appropriate, of gas distributor means. Thevelocity of transport gas into the riser is higher than the transportvelocity under the operating conditions, preferably from 2 to 15 m/s.

Generally, the polymer and the gaseous mixture leaving the riser areconveyed to a solid/gas separation zone. The solid/gas separation can beeffected by using conventional separation means. From the separationzone, the polymer enters the downcomer. The gaseous mixture leaving theseparation zone is compressed, cooled and transferred, if appropriatewith the addition of make-up monomers and/or molecular weightregulators, to the riser. The transfer can be effected by means of arecycle line for the gaseous mixture.

The control of the polymer circulating between the two polymerisationzones can be effected by metering the amount of polymer leaving thedowncomer using means suitable for controlling the flow of solids, suchas mechanical valves.

The operating parameters, such as the temperature, are those that areusual in gas-phase olefin polymerisation process, for example between 50to 120° C.

The process can be carried out under operating pressures of between 0.5and 10 MPa, preferably between 1.5 to 6 MPa.

Advantageously, one or more inert gases is/are maintained in thepolymerisation zones, in such quantities that the sum of the partialpressure of the inert gases is preferably between 5 and 80% of the totalpressure of the gases. The inert gas can be nitrogen or propane, forexample.

The various catalysts are fed up to the riser at any point of the saidriser. However, they can also be fed at any point of the downcomer. Thecatalyst can be in any physical state, therefore catalysts in eithersolid or liquid state can be used.

The usual additives, such as stabilizers and pigments, can also be addedto the polymers and compositions of the present invention.

As mentioned above, the propylene polymers according to the presentinvention are particularly suitable to prepare films and sheets, inparticular biaxially oriented films and sheets.

A further embodiment of the present invention provides laminatedarticles, in particular films and sheets, having improved stretchabilityand barrier properties, in particular moisture barrier properties. Thesaid articles are made of polymer compositions comprising theabove-mentioned polymers and a hard resin, such as polymers of coke ovengas, cracked naphtha, gas oil and terpene oil and terpene resin. Terpenecompounds are preferred. The hard resin is generally in an amount offrom 0.5 to 20% by weight, preferably form 0.5 to 15%, with respect tothe whole composition.

The laminated articles, i.e. films and sheets, of the present inventioncan be multilayered and at least one layer comprises the above-mentionedpropylene polymers or compositions.

The laminated articles, i.e. films and sheets, of the present inventionare obtained from the above-mentioned propylene polymers andcompositions by using the well-known processes for polyolefinfilms/sheets production.

The following examples are given in order to illustrate but not to limitthe present invention.

Characterizations

Test for the Extractability of the Electron Donor (ED) Compounds

A. Preparation of the Solid Catalyst Component

Into a 500 mL four-necked round flask, purged with nitrogen, 250 mL ofTiCl₄ are introduced at 0° C. While stirring, 10.0 g of microspheroidalMgCl₂.2.8C₂H₅OH (prepared according to the method described in example 2of U.S. Pat. No. 4,399,054 but operating at 3,000 rpm instead of 10,000)are introduced. 4.4 mmols of the selected electron donor compound arealso added.

The temperature is raised to 100° C. and maintained at said temperaturefor 120 min. Then, the stirring is discontinued, the solid product isallowed to settle and the supernatant liquid is siphoned off.

250 mL of fresh TiCl₄ are added. The mixture is reacted at 120° C. for60 min under stirring and, then, the supernatant liquid is siphoned off.The solid (A) is washed six times with anhydrous hexane (100 mL eachtime) at 60° C., dried under vacuum and analyzed for the quantitativedetermination of Mg and electron donor compound. The molar ratio ofelectron donor compound to Mg (ratio A) is thus determined:

B. Treatment of Solid A

In a 250 mL jacketed glass reactor with mechanical stirrer andfiltration septum are introduced under nitrogen atmosphere 190 mL ofanhydrous n-hexane, 19 millimoles of AlEt₃ and 2 g of the catalystcomponent prepared as described in A. The mixture is heated at 60° C.for 1 hour under stirring (stirring speed at 400 rpm). After said timethe mixture is filtered, washed four times with n-hexane at 60° C. andfinally dried under vacuum for 4 hours at 30° C. The solid is thenanalyzed for the quantitative determination of Mg and electron donorcompound. The molar ratio of electron donor compound to Mg (ratio B) isthus determined.

The extractability of the electron donor compound is calculatedaccording to the following formula: % of electron-donor compoundextracted=(Ratio A−Ratio B)/Ratio A.

Polymer Microstructure Analysis

50 mg of each xylene insoluble fraction are dissolved in 0.5 mL ofC₂D₂Cl₄.

The ¹³C NMR spectra are acquired on a Bruker DPX-400 (100.61 Mhz, 90°pulse, 12 s delay between pulses). About 3000 transients are stored foreach spectrum; mmmm pentad peak (21.8 ppm) is used as reference.

The microstructure analysis is carried out as described in literature(Polymer, 1984, 25, 1640, by Inoue Y et Al. and Polymer, 1994, 35, 339,by Chujo R. et Al.).

Determination of Xylene Insoluble Fraction (X.I.)

2.5 g of polymer are dissolved in 250 mL of o-xylene under stirring at135° C. for 30 minutes, then the solution is cooled to 25° C. and after30 minutes the insoluble polymer is filtered. The resulting solution isevaporated in nitrogen flow and the residue is dried and weighed todetermine the percentage of soluble polymer and then, by difference, theX.I. %.

TREF Method

TREF fractionation of the polymer is carried out by dissolving 1 g ofpropylene polymer in o-xylene at 135° C. and, slowly cooling (20 h) to25° C. in a column loaded with glass beads. Elution with o-xylene (600mL/h) is first carried out at 25° C. for 1 h to obtain a xylene-solublefraction. The column temperature is then raised from 25 to 95° C. at arate of 0.7° C./min without elution and the temperature is held at 95°C. for 2 h before eluting at this temperature for 1 hour to yield asingle fraction. Finally, elution is continued while raising thetemperature from 95 to 120° C. at a rate of 3° C./h, collectingindividual fractions at temperature intervals of 1° C. According to thepresent invention the stereoblock content is considered as the totalweight of the fractions, insoluble in xylene at 25° C., that are elutedat a temperature lower than 100° C. based on the total weight of thepolymer.

Melt Flow Rate (MFR)

Measured according to ISO 1133 (230° C., 2.16 kg).

Molecular Weight ({overscore (M_(n))}, {overscore (M_(w))} and{overscore (M_(z))})

Measured by way of gel permeation chromatography (GPC) in1,2,4-trichlorobenzene.

Determination of Polydispersity Index (P.I.)

This property is strictly connected with the molecular weightdistribution of the polymer under examination. In particular it isinversely proportional to the creep resistance of the polymer in themolten state. Said resistance called modulus separation at low modulusvalue (500 Pa), is determined at a temperature of 200° C. by using aparallel plates rheometer model RMS-800 marketed by RHEOMETRICS (USA),operating at an oscillation frequency which increases from 0.1 rad/secto 100 rad/sec. From the modulus separation value, one can derive theP.I. by way of the equation:P.I.=54.6×(modulus separation)^(−1.76)in which the modulus separation is defined as:modulus separation=frequency at G′=500 Pa/frequency at G″=500 Pawherein G′ is storage modulus and G″ is the loss modulus.Flexural Modulus

Measured according to ISO method 178.

Izod Impact Resistance

Measured according to ISO method 180/1A.

EXAMPLES 1 AND 2

Preparation of Solid Catalyst Component.

Into a 500 mL four-necked round flask, purged with nitrogen, 250 mL ofTiCl₄ are introduced at 0° C. While stirring, 10.0 g of microspheroidalMgCl₂.2.8C₂H₅OH (prepared according to the method described in example 2of U.S. Pat. No. 4,399,054 but operating at 3,000 rpm instead of 10,000)are introduced. As internal donors, a previously mixture ofdiisobutylphthalate (DIBP) and a blend of both the racemic form and mesoform of diethyl 2,3-(diisopropyl)succinate (DIBIPS) are also added. Theinternal donor content in the solid catalyst component is shown in Table1.

The temperature is raised to 100° C. and maintained for 120 minutes.Then, the stirring is discontinued, the solid product is allowed tosettle and the supernatant liquid is siphoned off.

250 mL of fresh TiCl₄ are added. The mixture is reacted at 120° C. for60 minutes and, then, the supernatant liquid is siphoned off. The solidis washed six times with anhydrous hexane (100 ml each time) at 60° C.

Polymerisation

In a 4 liter autoclave, purged with nitrogen flow at 70° C. for one our,75 mL of anhydrous hexane containing 7 mmols of AlEt₃,dicyclopentyldimethoxysilane as external electron-donor compound (theamount is reported in Table 1) and the solid catalyst component areintroduced in propylene flow at 30° C. The autoclave is closed, 1.5 NLof hydrogen are added and then, under stirring, 1.2 kg of liquidpropylene are fed. The temperature is risen to 70° C. in five minutesand the polymerisation is carried out at this temperature for two hours.The unreacted propylene is vented, the polymer is recovered and dried at70° C. under vacuum for three hours and, then, weighed and fractionatedwith o-xylene to determine the amount of the xylene insoluble (X.I.)fraction at 25° C. and its microstructure.

The polymerisation conditions are reported in Table 1.

EXAMPLE 3

Example 1 is repeated with except that in the polymerisation a mixtureof 70 wt % of dicyclopentyldimethoxysilane and 30 wt % ofcyclohexylmethyldimethoxysilane as outside electron-donor compound isused.

The polymerisation conditions are reported in Table 1.

EXAMPLE 4

Example 1 is repeated except that adduct of MgCl₂ with ethanol isdealcoholated as described in example 1 of European patent application728 769.

The polymerisation conditions are reported in Table 1.

COMPARATIVE EXAMPLE 1 (1c)

Preparation of Solid Catalyst Component.

The solid catalyst component is prepared according to above example 1,except that it contains a diether, namely9,9-bis(methoxymethyl)fluorene, as inside electron-donor compound in theplace of phthalate and succinate derivatives.

The internal donor content in the solid catalyst component is shown inTable 1.

Polymerisation

The polymerisation is carried out in continuous in a series of tworeactors equipped with devices for the transfer of the product comingfrom the reactor immediately preceding to the one immediately following.

In the gas phase the hydrogen and the monomer are analysed in continuousand fed in such a manner that the desired concentration will bemaintained constant.

A mixture of triethylaluminium activator anddicyclopentyldimethoxysilane as outside electron-donor compound iscontacted with the solid catalyst component in a container at 40° C. for13 minutes.

The catalyst is then transferred to a reactor containing an excess ofliquid propylene and prepolymerised at 20° C. for a period ranging from1.5 to 2 minutes ca.

The prepolymer is then transferred in another reactor where thepolymerisation occurs in gas phase to form fraction (A).

The product of the above reactor is fed to a second reactor in gas phaseto form fraction (B).

The polymerisation conditions are reported in Table 1.

TABLE 1 Example 1 2 3 4 1c Internal electron donor DIBIPS content, wt %4.54 6.79 6.79 4.63 0 DIBP content, wt % 12.8 11.68 11.68 6.63 0 Diethercontent, wt % 0 0 0 0 16.4 DIBIPS/DIBP molar ratio 0.35 0.63 0.63 0.75 0Solid catalyst component fed, g/h 8.2 7 6.6 6 — AlEt₃/solid catalystcomponent, g/g 10 13 14 13 6.1 AlEt₃/outside donor weight ratio 30 15 48 5.8 Polymerisation temperature, ° C. 70 70 70 75 70

The physical and mechanical properties of the polymers of examples 1 to4 and comparative example 1 are reported in Table 2. The mechanicalproperties are measured on injection-moulded samples. Plaques ofexamples and comparative example are stretched at temperatures rangingfrom 140 up to 155° C., in steps of 5° C.

TABLE 2 Example 1 2 3 4 1c mmmm, % >98 98.52 >98 98.61 98.43 {overscore(M)}_(w)/{overscore (M)}_(n) 9.2 9.6 8.7 — — {overscore(M)}_(z)/{overscore (M)}_(w) 4.2 4.1 4.8 — — Main elution peak — 114 —117 113 temperature, ° C. Stereoblock content up to — 5.2 — — 6.4 95°C., wt % Stereoblock content up to — 5.2 — 6.2 6.2 98° C., wt % Fractioneluted up to — — — 4.6 4.1 94° C., % MFR, g/10 min 3.5 3.5 2.6 2.6 3.5Xylene-soluble fraction, 1.7 1.6 1.4 1.5 1.3 wt % Polydispersity index4.8 5 4.9 4.6 5.5 Melting temperature, 163 163 163 165.7 162 ° C.Mechanical properties of the polymer Flexural modulus, MPa 1725 17701850 1780–  1810–  1940 1885 Izod impact resistance at 4.5 4.6 6 5.1 4.623° C., kJ/m²

EXAMPLE 5 AND COMPARATIVE EXAMPLE 2 (2c)

The polymer of example 4 and comparative example 1 are processed on aBOPP Stenter pilot line to produce a 20μ plain biaxially oriented film.Polymers are extruded through a flat die as a sheet that is cooled undercontrolled conditions on a casting unit. After leaving the casting unit,the sheet is re-heated to an appropriate temperature and then stretched4×1.1 in machine direction, by passing the film over a system of heatedrolls running at different speeds. The stretching in transverse machinedirection is achieved subsequently by a continuous drawing frame, whichis enclosed in a hot air oven. The film is pre-heating in this oven(=pre-heating temperatures—as indicated in table) and then stretched 8times in transverse machine direction by a system of chain-mounted clipsmoving on a diverging rail system. After the stretching, film isannealed and corona treated. Side edges are removed and finally the filmis winded on a roll. Speed of the line is 70 m/min.

TABLE 3 Example 5 2c Minimum oven pre-heating temperature, ° C. 162 164Optimum oven pre-heating temperature, ° C. 174 174 Deviation on a20μ-thick film, μm 1–2 0.5–3

The example 5 shows that, based on the deviation value, the filmaccording to the present invention has a more uniform thickness than thefilm of the comparative example. It is also shown that the polymer canbe stretched at a lower oven, pre-heating temperature still obtaining anacceptable film, compared to polymer of the comparative example 2,meaning that polymer according to the present invention is, easierprocessable compared to the comparative polymer.

EXAMPLES 6–8 AND COMPARATIVE EXAMPLE 3 (3c)

The compositions of examples 1–3 and comparative example 1 arecompression moulded into 1.0 mm plaques and subsequently biaxiallyoriented on a TM (Tenter Frame) long stretching frame. The stretchingoccurs simultaneously at a fixed stretch ratio of 7 times in machinedirection and 7 times in transverse machine direction.

Final film thickness of the biaxially oriented film is 20 μm.

Film properties are measured on the oriented film samples stretched atthe optimum stretching temperature, which corresponds to 0% failuretesting 5 plaques at each temperature.

The properties of the films are shown in Table 4.

TABLE 4 (Bi-oriented films from stretching frame) Example 6 7 8 3cElongation at break, % 26 28 28 21 Tensile stress at break, MPa 140 145146 135 Tensile modulus, MPa 2970 2730 2955 3180

Films according to the present invention show higher elongation at breakand higher tensile stress at break versus the comparative film.

1. A process for preparing propylene polymers comprising: 1) a contentof isotactic pentads (mmmm), measured by NMR, higher than 97%; 2) amolecular weight distribution, expressed by {overscore(M)}_(w)/{overscore (M)}_(n) ratio, equal to or higher than 6; and 3) avalue of {overscore (M)}_(z)/{overscore (M)}_(w) ratio equal to or lowerthan 5.5; said process comprising only one polymerisation stageconducted in presence of a Ziegler-Natta catalyst comprising: a solidcatalyst component comprising Mg, Ti, at least one halogen, and at leasttwo electron donor compounds, wherein said electron donor compoundscomprise at least one non-extractable succinate and at least oneextractable electron donor compound, wherein said non-extractablesuccinate is present in an amount from 15 to 50% by mol with respect toa total amount of said electron donor compounds, and saidnon-extractable succinate is selected from esters of succinic acidswhich are not extractable by more than 20% by mol; and wherein saidextractable electron donor compound is extractable by more than 30% bymol with respect to a total amount of said electron donor compounds; anorgano-metal compound; and an outside electron-donor, wherein saidoutside electron-donor is a highly stereoregulated electron donorcompound.
 2. The process of claim 1, wherein said esters of succinicacids are selected from succinates of formula (I):

wherein R₁ and R₂, are equal to or different from each other, and are aC₁–C₂₀ linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl,or alkylaryl, optionally containing heteroatoms; R₃ and R₄, are equal toor different from each other, and are a C₁–C₂₀ alkyl, cycloalkyl, aryl,arylalkyl, or alkylaryl, optionally containing heteroatoms, with theproviso that at least one of R₁, R₂, R₃, or R₄ is a branched alkyl; saidesters of succinic acids are stereoisomers of type (S,R) or (R,S) andare present in a pure form or racemic mixture.
 3. The process of claims1, wherein said extractable electron donor is selected from esters ofaromatic carboxylic acids.
 4. The process of claim 1, wherein saidoutside electron donor is selected from silanes of formula R_(a) ⁵R_(b)⁶Si(OR⁷)_(c), wherein a and b are integers from 0 to 2; c is an integerfrom 1 to 4, wherein (a+b+c) is 4; R⁵, R⁶ and R⁷ are alkyl, alkylene,cycloalkyl, or aryl radicals with 1 to 18 carbon atoms, optionallycontaining heteroatoms.